The long term goal of this study is to elucidate the cellular and molecular mechanisms(s) responsible for the decline in skeletal muscle performance with age. Age-related decreases in skeletal muscle mass, strength and quality, termed sarcopenia, contribute to physical disability and loss of independence. In this proposal it is postulated that the decline in DHPR and RyR1 number and function contributing to decline in skeletal muscle force with aging can be prevented by chronic exposure to elevated levels of autocrine/paracrine IGF-1 secretion. Exclusive overexpression of IGF-1 skeletal muscle prevents DHPR-RyR1 uncoupling at the T tubule-SR triadic junction. The preservation of sarcolemmal excitation-SR Ca2+ release signaling precludes decreases in SR calcium release and decline in contractile force in aging skeletal muscle. These studies will be performed in single fast- and slow-twitch muscle fibers from young (8 months), middle-age (18), and old (28) C57BL/6 and FVB and IGF-1 overexpressing mice (S1S2 transgenic mice). Contractile properties of both single fibers and fiber bundles will be measured together with intracellular calcium concentrations. DHPR-mediated intracellular calcium concentration elevations will be measured in single voltage-clamped muscle fibers. This approach allows for simultaneous analysis of the DHPR voltage sensing function and the increase in myoplasmic calcium concentration in response to DHPR-RyR1 interaction and RyR1 activation. The number of DHPR and RyR1 will be measured by high-affinity binding assay. Studies on apparent KD for specific ligands will determine a potential contribution of changes in pharmacological properties to alterations in receptor function. In single muscle fibers of different ages used for functional recording, DHPR and RyR1 mRNA levels will be quantitated. With this novel approach for skeletal muscle studies, age-related changes in DHPR and RyR1 function and their respective RNA concentrations will be obtained in the same muscle fiber. A direct involvement of IGF-1 in the regulation of DHPR and RyR1 gene transcription at different ages will be investigated.